Coupled neutronic core and subchannel analysis of nanofluids in VVER-1000 type reactor

This study is aimed to perform the coupled thermal-hydraulic/neutronic analysis of nanofluids as the coolant in the hot fuel assembly of VVER-1000 reactor core. Water-based nanofluid containing various volume fractions of Al2O3 nanoparticle is analyzed. WIMS and CITATION codes are used for neutronic simulation of the reactor core, calculating neutron flux and thermal power distribution. In the thermal-hydraulic modeling, the porous media approach is used to analyze the thermal behavior of the reactor core and the subchannel analysis is used to calculate the hottest fuel assembly thermal-hydraulic parameters. The derived conservation equations for coolant and conduction heat transfer equation for fuel and clad are discretized by Finite volume method and solved numerically using visual FORTRAN program. Finally the analysis results for nanofluids and pure water are compared together. The achieved results show that at low concentration (0.1 percent volume fraction) alumina is the optimum nanoparticles for normal reactor operation.

ANSYS-CFX simulation of the SRBTL test loop core with nanofluid coolant

In the present study, CFD calculations are presented for the three types of water-based nanofluids Al2O3/water, CuO/water and TiO2/water with 0.1% volume fraction. These calculations are done with ANSYS-CFX and as geometry the SRBTL test loop as scaled down test loop for a VVER-1000 reactor core design is used. The goal of this study is to evaluate the CFD program against the SRBTL test loop core as a scaled core for applying water-based nanofluids as coolant. ANSYS-CFX simulation data are validated against the RELAP5/MOD3.2 simulation data for pure water. This comparison shows a good agreement. The simulation results for the nanofluids and water including Re number, temperature, viscosity, pressure drop and heat transfer coefficient through the SRBTL test loop core are compared. The results of the comparisons show that the SRBTL test loop core is suitable to extract experimental data of water-based nanofluids for using them as coolant in the VVER-1000 reactor.

Neutronic simulation of a CANDU-6 reactor with heavy water-based nanofluid coolant

In recent years, extended studies are developed for investigation the effects of using nanofluids in NPP as coolant. CANDU-6 reactors have the potential to use nanofluid coolants because in these reactors, the moderator system is fully independent of the primary heat transport system. MCNPX code has been used for modelling and simulation of a CANDU-6 reactor containing a nanofluid as primary coolant. The variation of multiplication factor and total neutron flux distribution along a fuel channel, next to the central axis, has been investigated by using different nanofluids. In this analysis, heavy water-based nanofluids containing various volumetric percentages of Al2O3, TiO2, CuO, Ti, Cu, Zr, and Si nanoparticles were used. A typical CANDU-6 reactor was selected as reference for reactor core modelling. The results of the neutronic analysis show that Al2O3 nanofluids with 1% volumetric percentage are the most suitable coolant for CANDU-6 reactors which can increase the coolant heat transfer coefficient and consequently enhance the plant efficiency.

Spatial distribution of nanoparticles in PWR nanofluid coolant subjected to local nucleate boiling

Nanofluids have shown to be promising as an alternative for a PWR reactor coolant or as a safety system coolant to cover the core in the event of a loss of coolant accident. The nanoparticles distribution and neutronic parameters are intensively affected by the local boiling of nanofluid coolant. The main goal of this study was the physical-mathematical modeling of the nanoparticles distribution in the nucleate boiling of nanofluids within the viscous sublayer. Nanoparticles concentration, especially near the heat transfer surfaces, plays a significant role in the enhancement of thermal conductivity of nanofluids and prediction of CHF, Hide Out and Return phenomena. By solving the equation of convection-diffusion for the liquid phase near the heating surface and the bulk stream, the effect of heat flux on the distribution of nanoparticles was studied. The steady state mass conservation equations for liquids, vapors and nanoparticles were written for the flow boiling within the viscous sublayer adjacent the fuel cladding surface. The derived differential equations were discretized by the finite difference method and were solved numerically. It was found out that by increasing the surface heat flux, the concentration of nanoparticles increased.

Presenting and simulating an innovative model of liver phantom and applying two methods for dosimetry of it in neutron radiation therapy

AIM

A new model of liver phantom is defined, then this model is simulated by MCNPX code for dosimetry in neutron radiation therapy. Additionally, an analytical method is applied based on neutrons collisions and mathematical equations to estimate absorbed doses. Finally, the results obtained from two methods are compared to each other to justify the approach.

BACKGROUND

The course of treatment by neutron radiation can be implemented to treat cancerous tissues, although this method has not yet been widespread. The MIRD and the Stylized Family Phantom were the first anthropomorphic phantoms, although the representation of internal organs was quite crude in them. At present, a water phantom is usually used for clinical dosimetry.

MATERIALS AND METHODS

Each of the materials in an adult liver tissue including water and some organic compounds is decomposed into its constituent elements based on mass percentage and density of every element. Then, the accurate mass of every decomposed material of human liver tissue is correlated to masses of the phantom components.

RESULTS

The absorbed doses are computed by MCNPX simulation and analytical method in all components and different layers of this phantom.

CONCLUSIONS

Within neutron energy range of 0.001 eV-15 MeV, the calculated doses by MCNPX code are approximately similar to results obtained by analytical method, and the derived graphs of both methods approve one another. It is also concluded that through increasing the incident neutron energy, water receives the largest amounts of absorbed doses, and carbon, nitrogen and sulfur receive correspondingly less amounts, respectively.

Analysis of the small break loss of coolant accident in the VVER-1000/V446 reactor

In this paper, the analysis of a Small Break Loss of Coolant Accident (SBLOCA) in the VVER-1000/V446 nuclear power plant is presented. For a conservative analysis of the accident, the loss of power to the NPP and failure of one accumulator, and also of two emergency core cooling systems (ECCS) in loops 2 and 3 of the primary and secondary circuits are considered when SBLOCA has occurred. The RELAP5/MOD3.2 computer code has been used in performing the analyses. Two cases of accident scenarios as 25 mm and 100 mm breaks are analyzed. The results are in good agreement with those reported in the plant's FSAR. The results of liquid velocity show that in both cases, the flow of hot legs after the break is reversed, which provides the potential for reflux condensation phenomena. Furthermore, in the 25 mm break, the flow rate in the broken and intact side downcomer remains in the downward motion while in the 100 mm break, the broken and intact side flow rate changes to the reversed state alternatively.